Genesis 11:28

And it was when Nimrod had cast Abram into the furnace of fire because he would not worship his idol, and the fire had no power to burn him, that Haran's heart became doubtful, saying, If Nimrod overcome, I will be on his side: but if Abram overcome, I will be on his side. And when all the people who were there saw that the fire had no power over Abram, they said in their hearts, Is not Haran the brother of Abram full of divinations and charms, and has he not uttered spells over the fire that it should not burn his brother? Immediately (min yad, out of hand) there fell fire from the high heavens and consumed him; and Haran died in the sight of Terah his father, where he was burned in the land of his nativity, in the furnace of fire which the Kasdai had made for Abram his brother.

AND HARAN DIED IN THE PRESENCE OF HIS FATHER TERAH IN THE LAND OF HIS BIRTH IN UR OF THE CHALDEES. In accordance with the words of our Rabbis, Rashi wrote, “Terah accused his son Abram before Nimrod of having broken his idols, and he cast him into a fiery furnace. Meanwhile Haran waited and said to himself, ‘if Abram proves triumphant I will be on his side, and if Nimrod wins I shall be on his.’ When Abram was saved, they said to Haran, ‘On whose side are you?’ He replied, ‘I am on Abram’s side.’ They therefore cast him into the fiery furnace, and he was burnt to death. It is to this event that the name Ur Kasdim (fire of the Chaldees) alludes. Menachem ben Saruk, however, explained the word ur as meaning ‘valley.’ So also, Therefore glorify ye the Eternal ‘ba’urim’ (in the valleys), and also, ‘me’urath’ (the den of) the basilisk., 11:8. Every hole or deep cleft may be called ur.” This matter received by our Rabbis through tradition is the truth, and I will elucidate it.
Our father Abraham was not born in the land of Chaldaea. His ancestors were descendants of Shem, and Chaldaea and the whole land of Shinar were countries inhabited by the sons of Ham, and Scripture states, And he told to Abram the ‘Hebrew,’ not Abram the Chaldean. And it is further written, Your fathers dwelt in days of old beyond the river, Terah the father of Abraham, and the father of Nahor, the word mei’olam (of old) teaching that his origins were always from there. And again Scripture states, And I took your father Abraham from beyond the river. 3. Proof of the matter is that we find Nahor [Abraham’s brother] in Haran. Now if Terah’s place were in Ur of the Chaldees in the land of Shinar and Scripture relates that upon Terah’s going forth from Ur of the Chaldees he took with him only his son Abram, his grandson Lot the son of Haran, and Sarai his daughter-in-law, then Nahor was left in the land of Chaldaea, [and yet we find that he was in Haran, which is in the land of Mesopotamia, as explained further].
But the truth of the matter is that the country of the birth of Abraham’s ancestors was the land of Aram, which is beyond the River Euphrates; this was always the habitat of his ancestors. Thus Scripture says concerning the children of Shem, And their dwelling was from Mesha, as thou goest toward Sephar, unto the mountain of the east, this being a generic name applicable to all their countries, as it …

וימת הרן על פני תרח אביו, during his father’s lifetime. Something parallel occurred when the two sons of Aaron, Nadav and Avihu died during the lifetime of their father (Numbers 3,4).

בארץ מולדתו, the Torah mentions this seeing that Terach, Haran’s father did not die in the land where he had been born, but died in Charan after having emigrated there. This became the reason why Lot emigrated with his grandfather Terach from Ur Kasdim.

באור כשדים, a place known nowadays as Ur Kasdim, It could not have had that name at the time Terach and Avraham lived, as כשד the son of Nachor had not been born until later (Genesis 22,22) The offspring of this Kessed became were known as the Kasdim.

אור, the word means: “valley.” It occurs in this sense also in Isaiah 24,15 על כן באורים כבדו ה', “therefore honour the Lord in the valleys.” The view of our sages in the Midrash that the name is a reference to the place where Avraham was saved from the furnace of Nimrod is well known. (Bereshit Rabbah 38,13) They understand the word אור as meaning “fire.”